Methods for photoacoustic temperature measurement

ABSTRACT

TEMPERATURE MEASUREMENTS ARE CRITICAL TO VARIOUS ENERGY BASED THERAPEUTIC SYSTEMS, INCLUDING LASER, LIGHT, ELECTROMAGNETIC WAVE, AND HIGH INTENSITY FOCUSED ULTRASOUND BASED THERAPEUTIC SYSTEMS. THIS INVENTION DISCLOSES TECHNIQUES, APPARATUS AND METHODS FOR TEMPERATURE MEASUREMENTS OF SURGICAL TARGETS DURING VARIOUS THERAPEUTIC INTERVENTIONS WITH PHOTOACOUSTIC METHODS, ESPECIALLY WHEN DYNAMIC TEMPERATURE PULSES ARE GENERATED BY SELECTIVE PHOTOTHERMOLYSIS.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of application Ser. No.15/881,748, filed on Jan. 27, 2018, and entitled METHODS AND APPARATUSFOR OPTIMIZING SELECTIVE PHOTOTHERMOLYSIS, which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

This document relates to surgery techniques, apparatus and methods,including surgery techniques, apparatus and methods for selectivephotothermolysis (SP) surgeries. Some techniques can be applied togeneral surgical systems that heat up lesions in tissue, includinghigh-intensity-focused-ultrasound therapies.

SP, as described by Anderson and Parrish in a paper published by SCIENCEin 1983, utilizes short laser pulses to precisely control collateralthermal or mechanical damages around light-absorptive lesions withoutthe need of aiming a laser micro-beam at surgical targets. SP couldtarget not only nature chromophores within vasculature, skin, retina andother human tissues but also labeled single cells and theirultra-structures if both a tunable laser and cell-specific dye deliverysystem are available. A SP laser surgery has two distinct features, alarge surgical area and a short surgical laser pulse that deposits mostof the laser pulse energy into surgical targets. Thus non-surgicaltargets within a large surgical area remain healthy after SP while allsurgical targets are damaged. In contrast, laser surgeries of non-SPcategory include laser surgeries that use continuous wave (CW) laser tophotocoagulate surgical targets without limiting damaging area and lasersurgeries that use a small, high energy laser beam to non-selectivelyevaporate or sublime all illuminated tissue or tissue at the laser beamfocus. Typical non-SP laser surgery examples include photothermal cancertherapy with CW lasers, laser-assisted in-situ keratomileusis eyesurgery, and femtosecond laser-assisted cataract surgery. Typical SPlaser surgery examples include laser treatment of vascular malformation,some laser retinal photocoagulation surgeries, and some aestheticallaser surgeries such as laser tattoo removal.

Technical challenges associated with a SP laser surgery includemaximizing laser energy deposition ratios of surgical targets to naturechromophores, confining laser energy deposition into surgical targets,and optimizing laser pulse energy. Non-optimized SP laser parameters areassociated with unsatisfactory laser surgical outcomes. Although thecompromised SP laser surgical outcomes are well-known for decades, nogood solution exists in the prior art of SP.

BRIEF SUMMARY OF THE INVENTION

This document relates to surgery techniques, apparatus and methods foroptimizing selective photothermolysis (SP) surgeries. Some techniquescan be applied to general surgical systems that heat up lesions intissue, including high-intensity-focused-ultrasound therapies. It isnoted that a tunable light pulse in this document broadly means a lightpulse with tuning capabilities in its central wavelength, or light pulsewidth, or light pulse energy, or a combination of them.

In one aspect, a pulsed light SP surgical system comprises a tunablepulsed light source to produce pulsed surgical light beam under thecontrol of its control system; and a patient interface operable to be incontact with the target tissue. The patient interface comprises a lightdelivery unit, an acoustic detector, and an interface medium. The lightdelivery unit shapes the light beam profile, delivers light beam with anarticulated arm, adjusts the light beam diameter, and transmits thelight beam through the interface medium to a tissue surface. The pulsedlight beam excites photoacoustic waves that propagate through theinterface medium and are detected by the acoustic detector. The detectedphotoacoustic signals are digitized, analyzed by the control system forthe generation of surgical light pulses with optimal central wavelengthand light pulse energy for optimal SP surgical outcome.

In another aspect, a pulsed light SP surgical system comprises a tunablepulsed light source that can produce a pulsed surgical light beam or apulsed or modulated temperature-sensing light beam or both under thecontrol of its control system; and a patient interface operable to be incontact with the target tissue. The patient interface comprises a lightdelivery unit, an acoustic detector, and an interface medium. The lightdelivery unit shapes beam profiles of light beams, delivers light beamswith an articulated arm, adjusts diameters of light beams, and transmitslight beams through the interface medium to a tissue surface. The lightbeams excite photoacoustic waves that propagate through the interfacemedium and are detected by the acoustic detector. The detectedphotoacoustic signals are digitized, analyzed by the control system forthe generation of surgical light pulses with optimal central wavelength,pulse width and pulse energy for optimal SP surgical outcome.

In another aspect, a surgical planning system comprises a tunable pulsedlight source that can produce a subtherapeutic pulsed light beam or apulsed or modulated temperature-sensing light beam or both under thecontrol of its control system; and a patient interface operable to be incontact with the target tissue. The patient interface comprises a lightdelivery unit, an acoustic detector, and an interface medium. The lightdelivery unit shapes beam profiles of light beams, delivers light beamswith an articulated arm, adjusts diameters of light beams, and transmitslight beams through the interface medium to a tissue surface. The lightbeams excite photoacoustic waves that propagate through the interfacemedium and are detected by the acoustic detector. The detectedphotoacoustic signals are digitized, analyzed by the control system fordetermining optimal surgical light pulse parameters to be used byanother conventional pulsed light SP surgical system.

In another aspect, a pulsed radiation SP surgical system comprises twotunable radiation sources; a patient interface operable to be in contactwith the target tissue; and a control system. One tunable radiationsource produces a pulsed surgical radiation for heating up lesions intissue or extraneous contrast agents attached to lesions in tissue underthe control of the control system. Another tunable radiation sourceproduces a pulsed or modulated temperature-sensing radiation beam thatcan be absorbed by lesions in tissue or extraneous contrast agentsattached to lesions in tissue for excitations of photoacoustic wavesunder the control of the control system. The patient interface comprisesa radiation beam delivery unit for delivering radiation beams to tissue,and an ultrasonic detector to acquire photoacoustic signals excited byradiation beams. The control system acquires information from theultrasonic detector in the patient interface, analyzes information, andcontrols the generation of radiation beams with optimal centralwavelength or central frequency, pulse width, and pulse energy foroptimal SP surgical outcome.

In another aspect, a method for tuning surgical laser wavelength andoptimizing SP laser treatment of unknown surgical targets comprisesdetermining a series of surgical wavelength points for spectroscopicscanning and setting up both patient interface and acoustic detector;sending out multiple subtherapeutic surgical laser pulses for eachwavelength, acquiring and averaging photoacoustic signals, and repeatingfor all wavelength points; reconstructing 2-D, depth-resolved, relativeextinction coefficient information for all wavelength points;calculating relative extinction coefficient curve for all absorbers, andidentifying unknown surgical targets; calculating relative energydeposition ratio curves of unknown surgical targets to naturechromophores; and determining optimal surgical wavelengths for differenttypes of surgical targets.

In another aspect, a method for calibration of the temperature-dependentrelative logarithm function of Grüneisen parameter of tissue comprisesmeasuring the equilibrium temperature of tissue; measuring thephotoacoustic signals of a surgical target excited by atemperature-sensing laser pulse with a constant laser pulse energy;calculating a baseline signal as the logarithm of the amplitude of thephotoacoustic signal at the equilibrium temperature; sending only asurgical laser pulse and measuring excited photoacoustic signals;sending both a surgical laser pulse and a temperature-sensing laserpulse, and measuring the excited photoacoustic signals by dual pulses;calculating the logarithm of the amplitude of the photoacoustic signalexcited by the temperature-sensing laser pulse after a subtractionoperation and a logarithm operation; acquiring a data point aftersubtracting the baseline signal from the logarithm of the amplitude ofthe photoacoustic signal excited by the temperature-sensing laser pulse;determining whether there is a laser-induced cavitation; if not, waitingfor temperature returns to equilibrium; increasing surgical laser pulseto ki times; repeating the above procedures to acquire more data pointsfor the relative logarithm function of Grüneisen parameter of tissueuntil a laser-induced cavitation is observed; calculating absolutetemperature rise caused by surgical laser pulses and fitting the curveof the relative logarithm function of Grüneisen parameter of tissue withenough data points.

In another aspect, a method for photoacoustic sensing of the dynamictemperature of a surgical target in a tissue at the end of a shortsurgical laser pulse comprises measuring body temperature before lasersurgical intervention; sending a temperature sensing laser pulse with aconstant laser pulse energy, measuring the amplitude of the excitedphotoacoustic signal and calculating its logarithm as a baseline signal;sending only a surgical laser pulse and measuring the excitedphotoacoustic signal; sending both the surgical laser pulse and thetemperature-sensing laser pulse at the end of the surgical laser pulse,and measuring the excited photoacoustic signal by dual pulses;calculating the photoacoustic signal amplitude excited by thetemperature-sensing laser pulse at an unknown temperature at the end ofthe surgical laser pulse; separating the temperature-dependent part fromother temperature-independent parts with a logarithm operation;calculating the relative logarithm function value by subtracting thebaseline signal; determining the unknown temperature at the end of thesurgical laser pulse from the calibrated relative logarithm function ofGrüneisen parameter of tissue; and ending the temperature sensingoperation.

In another aspect, a method for measuring thermal relaxation time of asurgical target in tissue comprises measuring the body temperature andthe photoacoustic signal of a surgical target at body temperature with atemperature-sensing laser pulse and calculating the logarithm of thephotoacoustic signal amplitude as a base line signal; sending asubtherapeutic surgical laser pulse and measuring excited photoacousticsignal; sending both the subtherapeutic surgical laser pulse and thetemperature-sensing laser pulse with a precise delay time, measuringexcited photoacoustic signal of dual pulses, and calculating theamplitude of the photoacoustic signal excited by the temperature-sensinglaser pulse; separating the temperature-dependent part from othertemperature independent parts with a logarithm operation and calculatingthe relative logarithm function value by subtracting the baselinesignal; determining the temperature of the surgical target at theprecise delay time; waiting until surgical target temperature returns tobody temperature; determining whether enough delay time points have beenacquired for a curve-fitting; if not, repeating the above procedure formeasuring temperature at another delay time until enough delay timepoints have been acquired; fitting the curve of temperature versus delaytime and determining thermal relaxation time of the surgical target; andending the thermal relaxation time measurement operation.

In another aspect, a method for optimizing the surgical laser pulseenergy during a laser photocoagulation surgery comprises selecting asurgical target; measuring the surgical target's thermal relaxationtime; optimizing surgical laser pulse width according to the surgicaltarget's thermal relaxation time; sending only the surgical laser pulseand measuring the excited photoacoustic signal by the surgical laserpulse; sending both the surgical laser pulse and the temperature-sensinglaser pulse and measuring the excited photoacoustic signal by dualpulses; calculating the amplitude of the photoacoustic signal excited bythe temperature-sensing laser pulse; separating thetemperature-dependent part with a logarithm operation; calculatingrelative logarithm function value by subtracting the baseline signalacquired in the thermal relaxation time measurement step; determiningthe temperature of the surgical target; determining whether thetemperature reaches a predetermined surgical temperature ofphotocoagulation; if not, waiting for temperature recovery to bodytemperature and increasing surgical laser pulse energy; repeating theabove temperature measurement procedure until the temperature reachesthe predetermined surgical temperature of photocoagulation; and endingthe optimization of surgical laser pulse energy during a laserphotocoagulation surgery.

In another aspect, a method for optimizing the surgical laser pulseenergy during a laser photodisruption surgery comprises selecting asurgical target; sending the surgical laser pulse; measuring the excitedphotoacoustic signal; drawing one point for the curve of photoacousticsignal amplitude versus laser pulse energy; determining whether there isa laser-induced cavitation; if not, waiting for temperature recovery tobody temperature, increasing surgical laser pulse energy, and repeatingthe above procedure from the second step until the laser-inducedcavitation is observed and the surgical laser pulse energy is optimized.

In another aspect, a method for determining the surgical laser pulseenergy to achieve a predetermined temperature without laser surgerycomprises selecting a surgical target; measuring the surgical target'sthermal relaxation time; optimizing surgical laser pulse width accordingto the surgical target's thermal relaxation time; sending asubtherapeutic surgical laser pulse and measuring excited photoacousticsignal; sending both the subtherapeutic surgical laser pulse and thetemperature-sensing laser pulse; measuring excited photoacoustic signalby dual pulses; calculating the amplitude of the photoacoustic signalexcited by the temperature sensing laser pulse; separating thetemperature-dependent part with a logarithm operation and calculatingrelative logarithm function value by subtracting the baseline signalacquired in previous thermal relaxation time measurement step;calculating the dynamic temperature rise due to the subtherapeuticsurgical laser pulse and the required surgical laser pulse energy forheating the surgical target to a predetermined temperature; and endingthe optimization of surgical laser pulse energy to achieve apredetermined temperature without laser surgery.

In yet another aspect, a method for an optimized SP laser surgery withskin cooling comprises tuning the surgical laser wavelength to maximizeSP surgical effects; optimizing surgical laser pulse width; optimizingsurgical laser pulse energy; measuring body temperature; applying atemperature-sensing laser pulse; measuring excited photoacoustic signalof an epidermis target; adjusting skin cooling parameter; applying skincooling and a delayed temperature-sensing laser pulse; measuringtemperature of the epidermis target; determining whether the epidermistarget has been cooled to a predetermined temperature; if not, returningto the above procedure of adjusting skin cooling parameter and measuringepidermis target temperature until it is cooled to a predeterminedtemperature; and performing an optimized SP laser surgery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a pulsed light selective photothermolysis(SP) surgical system wherein the inclusion of an acoustic detector isthe key for optimizing SP.

FIGS. 2-10 show examples of patient interfaces with differentconfigurations to facilitate optimized selective photothermolysis withlasers.

FIG. 11 shows an example of wavelength tuning operation for optimizingselective photothermolysis of unknown pigments.

FIG. 12 shows an example of calibrating a temperature-dependent relativelogarithm function of Grüneisen parameter of a tissue.

FIG. 13 shows an example of dynamic temperature-sensing operation of asurgical target in a tissue after heating by a short surgical laserpulse.

FIG. 14 shows an example of optimizing surgical laser pulse width by invivo measuring thermal relaxation time of a surgical target in a tissue.

FIG. 15 shows an example of in vivo surgical laser pulse energyoptimization for laser photocoagulation during a laser surgery.

FIG. 16 shows an example of in vivo surgical laser pulse energyoptimization for laser photodisruption during a laser surgery.

FIG. 17 shows an example of determining optimal surgical laser pulseenergy to achieve a predetermined temperature without performing lasersurgery.

FIG. 18 shows an example of operations for an optimized selectivephotothermolysis laser surgery with skin cooling.

DETAILED DESCRIPTION OF THE INVENTION

It is important to understand laser-tissue interaction mechanisms ofselective photothermolysis (SP) laser surgery before addressing itsclinical problems. Both thermal and mechanical damages could be utilizedin SP. Initially, no measurable effects could be caused when tissuetemperature is elevated to 37°-42° C. by SP laser pulses. Tissue is inhyperthermia status when temperature keeps rising to 42°-50° C. A largeportion of tissue might undergo necrosis if the hyperthermia lasts forseveral minutes. Enzyme activity reduction and cell immobility startfrom 50° C. Denaturation of proteins and collagen occurs at 60° C. andleads to coagulation of tissue and necrosis of cells. Cell membranepermeability will significantly increase at 80° C. Water molecules willbe vaporized at 100° C. It may lead to cavitation and tissue mechanicalrupture by acoustic shock-waves associated with the laser-inducedcavitation. Another type of mechanical damage could be caused by thestrong photoacoustic waves generated by light absorbers upon the shortlaser pulse excitations. Major SP commercial applications include lasertattoo removal, laser treatment of vascular malformation and laserretinal photocoagulation.

Laser tattoo removal is usually performed with very short laser pulsesin nanosecond or even picosecond regime. However, the proposedmechanisms behind laser tattoo removal have their physical, chemical andbiological origins. Pigmented particles of tattoo will experience rapidtemperature rise and volume expansion upon the energy deposition orexcitation by a short laser pulse. However, most of the temperature riseand the volume expansion will be lost after a short period of time,determined by thermal relaxation time (time taken for 50% of heat energyto be dissipated away) of these particles. Photoacoustic waves aregenerated along with the volume changes of these particles. Laser energyis transformed into both thermal energy and mechanical energy carried bythe photoacoustic waves. In many cases, large laser pulse energyabsorbed by pigmented particles may cause optical breakdown, plasmageneration, chemical reactions between plasma and pigmented particles,cavitation and generation of acoustic shock-waves. These pigmentedparticles might be pyrolytically altered or shattered into smallerparticles by the photoacoustic waves and acoustic shock-waves. Hostingcell necrosis and surround tissue damage might be induced thermally andmechanically during this process. In the end, the wound healing processmight remove partial pigmented particles through rephagocytosis andalter the dermal scattering coefficients of the affected tissue, whichmight make the deeper pigmented particles less visible.

For laser tattoo removal application, the color of a tattoo depends onmany factors including its optical absorption spectrum, opticalscattering and absorption coefficients of the tissue above and below thepigments, the depth of the pigment and anatomical location of thepigments. It was reported that tattoos with significantly differentoptical absorption spectra could present themselves with the same colorto naked eyes. Obviously, current practice of selecting surgical laserwavelength based on the color of a tattoo is not justified. On the otherhand, there are only a handful of laser wavelengths (694 nm ruby laser,755 nm Alexandrite, 1064 nm Nd:YAG and 532 nm second harmonic Nd:YAG)available in the market for laser tattoo removal. Even if the absorptionspectra of the pigments of the tattoo is happened to be known, there aresignificant chances that it is not matching with any existing laser inthe market. Anderson and Parrish envisioned a tunable laser for SP in1983. However, such a laser is not available yet because nobody knowswhat wavelength should be adjusted to. Additionally, the selection oftreatment laser pulse energy is also determined by the clinician'sexperience. Both clinical problems of laser tattoo removal are addressedby this invention.

Laser treatment of vascular malformation starts from the argon laser(488 and 514 nm) treatment of port-wine stain (PWS) in 1970s. Theblue-green light of argon lasers is preferentially absorbed byhemoglobin within the PWS blood vessels. The deposited laser pulseenergy into the vessels is largely converted to heat, causing thrombosisand destruction of the PWS blood vessels. The first generation argonlaser had relatively long pulse duration (˜0.01 s), which causednon-specific tissue thermal damage of epidermis tissue. Thus, scarringwas a frequent complication of the first generation argon lasertreatment of PWS. Selective photothermolysis of PWS blood vessels wasachieved by the first generation pulsed dye laser (PDL) (577 nm or 585nm, 0.45 milliseconds) that selectively photocoagulated PWS bloodvessels and spared overlying epidermal tissue with a low incidence ofside effects. As PDL laser energy is deposited in the intraluminal blooddue to selective absorption of hemoglobin, the heat diffuses to thevessel wall and causes vascular wall necrosis and subsequentextravasation of red blood cells into the adjacent dermis. Dermalcollagen fills the space of photocoagulated PWS vessels via woundhealing process. The removal of photocoagulated PWS lesions leads to theblanching of PWS. The second generation PDL technique adopts larger spotsizes, higher energy densities, variable pulse durations, and dynamiccooling for more effective treatment of PWS. Currently, the secondgeneration PDL with dynamic pulse duration and dynamic epidermal coolingby liquid cryogen sprays is the treatment of choice for PWSs. However,the laser has to be operated by experienced clinicians who adjust laserpulse width and laser pulse energy based on their experiences. In fact,the average success rate for full clearance is below 20%. The selectionof pulsed laser parameters is the most challenging clinical problem inlaser treatment of vascular malformation.

The above mentioned clinical problems in laser tattoo removal and lasertreatment of vascular malformation are obviously related to thedistributions of light absorbers inside of tissue. Some experiencedclinician takes advantage of the sounds generated during laser andtissue interaction to help laser tattoo removal surgery. However, humanonly hears sound wave between 20 Hz-20,000 Hz. For laser tattoo removal,laser tissue interaction does generate high-frequency ultrasonic waves.Most of their frequency components are far beyond 20,000 Hz. In otherwords, most of useful information are completely ignored. By adding anultrasonic detector to “hear” the responses from tissue under a SP lasersurgery, this invention is able to address the above-mentioned clinicalproblems. The science behind the photoacoustic waves during laser-tissueinteractions is photoacoustics, the key technique for this invention.

Photoacoustic techniques originate from Alexander Graham Bell whodiscovered photoacoustic effect in 1880. The generation of photoacousticwave consists of the following stages including conversion of theabsorbed pulsed or modulated radiation into heat energy, temporal changeof temperature that rises as laser pulse energy is absorbed and fallswhen laser pulse ends and the heat dissipates, and volume expansion andcontraction following these temperature changes, which generate pressurechanges (i.e. photoacoustic wave). Hordvik et al. reported photoacoustictechnique for determining optical absorption coefficients in solids in1977. Photoacoustic spectroscopy was applied to a wide variety ofconventional spectroscopic measurements as reviewed by West et al. in1983. More recent developments of photoacoustic techniques weremotivated by biomedical imaging applications. Major photoacoustictechnique developments in the biomedical imaging field include theinventions of acoustic-resolution & optical-resolution photoacousticmicroscopies by Maslov et al. and the Fabry-Perot photoacoustic sensorbased photoacoustic tomography by Zhang et al. The significantlyimproved image performance (sensitivity, resolution, depth and speed) ofthe above photoacoustic imaging systems and improvements of acoustictransducer arrays by industry for various photoacoustic tomographyconfigurations generate high impacts in biology and medicine.

The penetration of photoacoustic techniques into SP laser surgery isvery limited. Nobody tried to build a wavelength tunable laser and applysuch a laser for tattoo removal with photoacoustics. Selecting laserwavelength in laser treatment of vascular malformation might be lesscritical than in laser tattoo removal. But it is still a verychallenging task to optimize other parameters of laser surgical systemsfor laser treatment of vascular malformation. In fact, a SP lasersurgery does not necessary get rid of surgical targets or change thespatial location of surgical targets right after a SP laser surgery. Itrequires a long wound healing process to remove damaged tissues throughrephagocytosis. Photoacoustic imaging of lesions before and right afterSP laser surgery almost presents no changes in lesion images. Thus, asimple photoacoustic imaging of lesions has no value for optimizing SPlaser surgery. Viator et al. demonstrated the feasibility of imagingdeep port-wine stain lesions with photoacoustic tomography withoutfurther application of the acquired lesion depth information foroptimizing laser treatment of port-wine stain. In order to optimizelaser treatment of port-wine stain in children, Rao et al. proposed toimage the port-wine stain vessel size and depth in child patients withoptical-resolution photoacoustic microscopy, construct physical model ofport-wine stain lesions with lesion information, and derive optimallaser treatment parameters (pulse width and pulse energy) with massivecomputer simulations. Other imaging modalities such as optical Dopplertomography and optical coherence angiography relied on blood flow orblood flow induced optical speckles to acquire information of port-winestain lesions. However, the lack of blood flow right after laser surgerycould not confirm full photocoagulation of lesion vessels. It washypothesized that partially coagulated lesion vessels could remainrefractory after laser treatment. Another limitation of these opticalimaging modalities is their shallow imaging depth of 1-2 mm. Incontrast, this invention takes simple experimental approaches to addressthe SP clinical problems.

The disclosed techniques, methods and apparatus of this invention arebased on the physical principle of photoacoustic effect and itstemperature-dependence. In early literature of photoacoustic techniques,the temperature-dependent photoacoustic effect was utilized in a rangeof temperature related measurements including measuring flametemperature and measuring solid thermal diffusivity. Esenaliev et al.reported real-time optoacoustic monitoring of temperature in ex vivocanine tissues in 1999. Larin et al. reported optoacoustic lasermonitoring of cooling and freezing of ex vivo canine liver in 2002. Shahet al. reported photoacoustic temperature monitoring of ex vivo porcinetissue in 2008. Oraevsky et al. described optoacoustic imaging methodsfor medical diagnosis and real time optoacoustic monitoring of change intissue properties, and an improved temperature calibration method inU.S. Pat. Nos. 5,840,023A, 6,309,352B1, and US2015/0216420A1. In acontinuous-wave laser thermal therapy described by Oraevsky et al.,tissue temperature varies very slowly. The continuous-wave laser has noeffect on an asynchronous photoacoustic temperature-sensing process. Incontrast, short surgical light pulses of a SP surgery system heat up asurgical target within its short pulse duration and the surgical targetcools down quickly. Measuring a dynamic temperature rise due to energydeposition of a short surgical laser requires the temperature-sensinglight pulse to be synchronized to the surgical light pulse with an exactshort time delay. Additionally, the strong surgical light pulsesgenerate strong photoacoustic signals upon absorption by light absorbersin tissue. The photoacoustic signal excited by the surgical light pulseinterferes with the photoacoustic signal excited by thetemperature-sensing light pulse. Both issues, which make thephotoacoustic temperature measurement methods described by Oraevsky etal. and others in prior art invalid for SP surgeries with short surgicallight pulses, are addressed by methods of this invention.

In summary, the prior art is deficient in methods to address clinicalproblems in SP surgeries such as laser tattoo removal and lasertreatment of vascular malformation. The surgery techniques, apparatusand methods are disclosed below to fill the gaps between the sciencetheory of SP and clinical practices.

As an example, FIG. 1 shows an example of a revolutionary, pulsed lightSP surgical system wherein the inclusion of an acoustic detectordifferentiates it from a conventional SP light surgical system. This SPpulsed light surgical system comprises a tunable pulsed light source1100 to produce light beams 1010 under the control of its control system1110; and a patient interface 1200 operable to be in contact with atissue 1000. In one implementation of FIG. 1, the light beams 1010comprise only a surgical pulsed light beam. The pulse width of thepulsed light beam is less than 10⁻⁷ seconds, or less than 10⁻⁸ seconds,or less than 10⁻⁹ seconds in order to efficiently excite photoacousticsignals. The patient interface 1200 comprises a light delivery unit1210, an acoustic detector 1220, and an interface medium 1230. The lightdelivery unit 1210 shapes the light beam profile, delivers the lightbeam with an articulated arm, adjusts the light beam diameter andtransmits the light beam through the interface medium 1230 to a tissue1000 surface. The pulsed light beam 1010 excites photoacoustic waves1020 that propagate through the interface medium 1230 and are detectedby the acoustic detector 1220. The detected photoacoustic signals 1030are digitized, analyzed in the control system 1110 for the control ofthe tunable pulsed light beam 1100. It is noted that a tunable lightsource in this document broadly means a light source with tuningcapabilities in its central wavelength, or light pulse width, or lightpulse energy or a combination of them. Tunable light source itself isnot difficult to make. However, the missing part is how the centralwavelength and other surgical light pulse parameters should be tunedaccording to surgical targets in tissue. The inclusion of an acousticdetector is exactly the missing part in prior art of SP surgeries. Theinclusion of an acoustic detector makes sense to the utilization of atunable light source in SP surgeries for the first time. Both thetunable light source and the acoustic detector make an optimized SPsurgery possible, a goal that has been desired for decades.

In order to fully utilize the disclosed methods below for optimized SPsurgical outcomes, it is desirable to utilize a more advanced tunablelight source 1100, which can produce a surgical light pulse or atemperature-sensing light beam or both under the control of its controlsystem 1110. For most of implementations of FIG. 1, thetemperature-sensing light beam comprises temperature-sensing lightpulses that have a tunable time delay relative to surgical light pulses.However, the temperature-sensing light beam could be an intensitymodulated light beam to excite photoacoustic waves when depth-resolvedtissue information is not required for an application, or a chirpedintensity-modulated light beam to allow a very low-resolution depthdiscrimination. The pulse width of the temperature-sensing light pulsesis less than 10⁻⁷ seconds, or less than 10⁻⁸ seconds, or less than 10⁻⁹seconds in order to efficiently excite photoacoustic signals. Thecentral wavelength and pulse width of the temperature-sensing light beamcould be fixed for some implementations. The temperature-sensing lightpulse energy is of subtherapeutic level. For the tunable light source1100, its tuning capabilities should match with the needs of a specificSP surgery application. The most practical implementation of such a moreadvanced tunable light source is to integrate a tunable surgical lightsource unit and a tunable temperature-sensing light source unit into asingle package with a shared power supply subsystem, a shared coolingsubsystem and a shared control system 1110. The light beams of the lightsource units need to be combined, and sent out from the same lightoutput port. In some implementations, it is preferable to use alow-cost, fixed-wavelength, pulsed solid state laser to generate thetemperature-sensing light beam.

Yet another implementation of FIG. 1 could be a surgical planning systemthat provide optimized surgical laser parameters for other conventionalpulsed light SP surgical systems. Such a surgical planning systemcomprises a tunable pulsed light source that can produce asubtherapeutic pulsed light beam or a pulsed or modulatedtemperature-sensing light beam or both under the control of its controlsystem; and a patient interface operable to be in contact with thetarget tissue. The patient interface comprises a light delivery unit, anacoustic detector, and an interface medium. The light delivery unitshapes beam profiles of light beams, delivers light beams with anarticulated arm, adjusts diameters of light beams, and transmits lightbeams through the interface medium to a tissue surface. The light beamsexcite photoacoustic waves that propagate through the interface mediumand are detected by the acoustic detector. The detected photoacousticsignals are digitized, analyzed by the control system for determiningoptimal surgical light pulse parameters to be used by anotherconventional pulsed light SP surgical system. The advantage of such asurgical planning system is that its laser pulse repetition rate couldbe much higher than a surgical system and the time for acquiringoptimized surgical laser parameters is much shorter.

The key of this invention is the inclusion of an ultrasonic transducerin a conventional SP surgery system. A pulsed light SP surgical systemof FIG. 1 could be generalized as a pulsed radiation SP surgical systemby replacing the surgical light pulse with any form of radiation (radiowaves, microwaves, infrared light, visible light, Ultraviolet, X-rays,Gamma rays) pulse that heats up lesions or extraneous contrast agentsattached to lesions in tissue, replacing the temperature-sensing lightpulse with any form of pulsed or modulated radiation (radio waves,microwaves, infrared light, visible light, Ultraviolet, X-rays, Gammarays) that can be absorbed by lesions in tissue or extraneous contrastagents attached to lesions in tissue, and effectively excitephotoacoustic waves, and replacing the light delivery unit in thepatient interface with a radiation beam delivery unit for delivering aradiation beams to tissue. All techniques and methods for FIG. 1 applyto the generalized radiation SP surgical system. The examples presentedbelow are mostly based on pulsed laser surgical systems because lasertattoo removal and laser treatment of vascular malformation are majorconcerns of this invention.

FIGS. 2-10 show examples of patient interfaces with differentconfigurations to facilitate optimized SP laser surgery. FIG. 2 shows aschematic example of a patient interface comprising a single elementultrasonic transducer 2200, and an interface medium 2300 in acousticcontact with tissue 2400. Because a light delivery unit that should beshown in the patient interface is no different from that of aconventional laser SP system, the light delivery unit is skipped in FIG.2 for simplicity. Laser beams 2100 (a surgical laser beam, or atemperature-sensing laser beam, or both) can be selectively delivered tothe tissue 2400 surface according to the requirements of the methods. Insome implementations, laser beams 2100 could only comprise a surgicallaser beam. The single element ultrasonic transducer 2200 is positionedto detect photoacoustic waves without blocking laser beams 2100. Thetransducer 2200 could be a traditional ultrasonic transducer or onebased on optical detection techniques. The interface medium 2300 allowsthe transmission of laser beams and photoacoustic waves with minimumenergy loss. The interface medium 2300 could be saved in a moresimplified configuration where the single element ultrasonic transduceris in direct acoustic contact with tissue at a tissue surface areaimmediately next to a tissue surface area illuminated by the laserbeams. One advantage of this simplified configuration is that it maysimultaneously allow the delivery of skin cooling agent through freespace. Spectroscopic photoacoustic signals are acquired by the singleelement ultrasonic transducer 2200 from a one-dimensional,depth-resolved space in the tissue, and are digitized and analyzed bythe control system 1110 of FIG. 1.

FIG. 3 shows another schematic example of a patient interface comprisinga linear arrayed ultrasonic transducer 3200 and an interface medium 3300in acoustic contact with tissue 3400. Because a light delivery unit thatshould be shown in the patient interface is no different from that of aconventional laser SP equipment, the light delivery unit is skipped inFIG. 3 for simplicity. Laser beams 3100 (a surgical laser beam, or atemperature-sensing laser beam, or both) can be selectively delivered tothe tissue 3400 surface according to the requirements of the methods.The linear arrayed ultrasonic transducer 3200 is positioned to detectphotoacoustic waves without blocking laser beams 3100. The lineararrayed transducer 3200 could be a traditional ultrasonic transducer orone based on optical detection techniques. The interface medium 3300allows the transmission of laser beams and photoacoustic waves withminimum loss. The interface medium 3300 could also be saved in a moresimplified configuration where the linear arrayed ultrasonic transduceris in direct acoustic contact with tissue at a tissue surface areaimmediately next to a tissue surface area illuminated by the laser beamsdelivered through free space. One advantage of this simplifiedconfiguration is that it may simultaneously allow the delivery of skincooling agent through free space. Spectroscopic photoacoustic signalsare acquired by the linear arrayed ultrasonic transducer 3200 from atwo-dimensional, depth-resolved space in the tissue, and are digitizedand analyzed by the control system 1110 shown in FIG. 1.

FIG. 4 shows another schematic example of a patient interface comprisinga linear arrayed ultrasonic transducer 4200, an interface medium 4300 inacoustic contact with tissue 4400, and a rotational stage 4500 thatmounts the linear arrayed ultrasonic transducer 4200 and the interfacemedium 4300 and rotates around the central axis of the illuminated ovalarea on tissue surface for the acquisition of a three-dimensional tissueinformation. The arrows 4600 show the rotational direction of therotation stage 4500. Because a light delivery unit that should be shownin the patient interface is no different from that of a conventionallaser SP system, the light delivery unit is skipped in FIG. 4 forsimplicity. Laser beams 4100 (a surgical laser beam, or atemperature-sensing laser beam, or both) can be selectively delivered tothe tissue 4400 surface according to the requirements of the methods.Laser beams 4100 are delivered with a flexible multimode fiber or aflexible fiber bundle and accessory optics (not shown in FIG. 4) toallow rotation. The linear arrayed ultrasonic transducer 4200 ispositioned to detect photoacoustic waves without blocking laser beams4100. The linear arrayed transducer 4200 could be a traditionalultrasonic transducer or one based on optical detection techniques. Theinterface medium 4300 allows the transmission of laser beams andphotoacoustic waves with minimum loss. The interface medium 4300 couldalso be saved in a more simplified configuration where the lineararrayed ultrasonic transducer is in direct acoustic contact with tissueat a tissue surface immediately next to a tissue surface areailluminated by the laser beams delivered through free space. Oneadvantage of this simplified configuration is that it may simultaneouslyallow the delivery of skin cooling agent through free space.Spectroscopic photoacoustic signals are acquired by the linear arrayedultrasonic transducer 4200 from a three-dimensional, depth-resolvedspace in the tissue, and are digitized and analyzed by the controlsystem 1110 shown in FIG. 1.

FIG. 5 shows another schematic example of a patient interface comprisinga single element ultrasonic transducer 5200, an acoustic wave reflector5500, and an interface media 5300 in acoustic contact with tissue 5400.Because a light delivery unit that should be shown in the patientinterface is no different from that of a conventional laser SP system,the light delivery unit is skipped in FIG. 5 for simplicity. Laser beams5100 (a surgical laser beam, or a temperature-sensing laser beam, orboth) can be selectively delivered to the tissue 5400 surface accordingto the requirements of the methods. The single element ultrasonictransducer 5200 is positioned to detect photoacoustic waves reflected bythe acoustic reflector 5500 without blocking laser beams 5100. The usageof an acoustic reflector 5500 allows the laser beams and the transduceron the same side of tissue without blocking each other. The singleelement ultrasonic transducer 5200 could be a traditional ultrasonictransducer or one based on optical detection techniques. The interfacemedium 5300 allows the transmission of laser beams and photoacousticwaves with minimum loss. Spectroscopic photoacoustic signals areacquired by the single element ultrasonic transducer 5200 from aone-dimensional, depth-resolved space in the tissue, and are digitizedand analyzed by the control system 1110 shown in FIG. 1.

FIG. 6 shows another schematic example of a patient interface comprisinga linear arrayed ultrasonic transducer 6200, an acoustic reflector 6500,and an interface media 6300 in acoustic contact with tissue 6400.Because a light delivery unit that should be shown in the patientinterface is no different from that of a conventional laser SP system,the light delivery unit is skipped in FIG. 6 for simplicity. Laser beams6100 (a surgical laser beam, or a temperature-sensing laser beam, orboth) can be selectively delivered to the tissue 6400 surface accordingto the requirements of the methods. The linear arrayed ultrasonictransducer 6200 is positioned to detect photoacoustic waves reflected bythe acoustic reflector 6500. The usage of an acoustic reflector 6500allows the laser beams and the transducer on the same side of tissuewithout blocking each other. The linear arrayed ultrasonic transducer6200 could be a traditional ultrasonic transducer or one based onoptical detection techniques. The interface medium 6300 allows thetransmission of laser beams and photoacoustic waves with minimum loss.Spectroscopic photoacoustic signals are acquired by the linear arrayedultrasonic transducer 6200 from a two-dimensional, depth-resolved spacein the tissue, and are digitized and analyzed by the control system 1110shown in FIG. 1.

FIG. 7 shows another schematic example of a patient interface comprisinga linear arrayed ultrasonic transducer 7200, an acoustic reflector 7500,an interface media 7300 in acoustic contact with tissue 7400, and arotational stage 7600 that mounts the linear arrayed ultrasonictransducer 7200, the acoustic reflector 7500 and the interface medium7300, and rotates around the axis of the laser beams. The arrows 7700show the rotational direction of the rotation stage 7600. Because alight delivery unit that should be shown in the patient interface is nodifferent from that of a conventional laser SP system, the lightdelivery unit is skipped in FIG. 7 for simplicity. Laser beams 7100 (asurgical laser beam, or a temperature-sensing laser beam, or both) canbe selectively delivered to the tissue 7400 surface according to therequirements of the methods. The linear arrayed ultrasonic transducer7200 is positioned to detect photoacoustic waves reflected by theacoustic reflector 7500. The usage of acoustic reflector 7500 allows thelaser beams and the transducer on the same side of tissue withoutblocking each other. The linear arrayed ultrasonic transducer 7200 couldbe a traditional ultrasonic transducer or one based on optical detectiontechniques. The interface medium 7300 allows the transmission of laserbeams and photoacoustic waves with minimum loss. Spectroscopicphotoacoustic signals are acquired by the linear arrayed ultrasonictransducer 7200 from a three-dimensional, depth-resolved space in thetissue, and are digitized and analyzed by the control system 1110 shownin FIG. 1.

FIG. 8 shows another schematic example of a patient interface comprisinga Dammann grating 8200, a 2-D arrayed ultrasonic transducer 8400, and aninterface medium 8500 in acoustic contact with tissue 8600. Because alight delivery unit that should be shown in the patient interface is nodifferent from that of a conventional laser SP system, the lightdelivery unit is skipped in FIG. 8 for simplicity. Laser beams 8100 (asurgical laser beam, or a temperature-sensing laser beam, or both) canbe selectively delivered to the tissue 8600 surface according to therequirements of the methods. The laser beams are transformed into 2-Darrayed laser beams 8300 by a Dammann grating 8200. 2-D arrayed laserbeams pass through the free space not being taken by the 2-D arrayedultrasonic transducer 8400 and the interface medium 8500 before reachingthe tissue 8600. The excited photoacoustic waves are detected by the 2-Darrayed ultrasonic transducer 8400. The 2-D arrayed ultrasonictransducer 8400 could be a traditional ultrasonic transducer or onebased on optical detection techniques. The interface medium 7300 allowsthe transmission of laser beams and photoacoustic waves with minimumloss. Spectroscopic photoacoustic signals 8700 are acquired by the 2-Darrayed ultrasonic transducer 8400 from a three-dimensional,depth-resolved space in the tissue, and are digitized and analyzed bythe control system 1110 shown in FIG. 1.

FIG. 9 shows another schematic example of a patient interface comprisinga dichroic mirror 9200, a scanning lens 9500, a 2-D Galvo scanner 9600,and a Fabry-Perot sensor 9300 in acoustic contact with a tissue 9400.Because a light delivery unit that should be shown in the patientinterface is no different from that of a conventional laser SP system,the light delivery unit is skipped in FIG. 9 for simplicity. Laser beams9100 (a surgical laser beam, or a temperature-sensing laser beam, orboth) can be selectively delivered to the tissue 9400 surface accordingto the requirements of the methods. Both the dichroic mirror 9200 andthe Fabry-Perot sensor 9300 are transparent for the laser beams 9100 (asurgical laser beam, or a temperature-sensing laser beam, or both). Anultrasonic-wave-detection laser beam 9700 is scanned by the 2-D Galvoscanner 9600 and the scanning lens 9500, and reflected by the dichroicmirror 9200 to the Fabry-Perot sensor 9300 for the detection ofphotoacoustic waves. The Fabry-Perot sensor 9300 comprises of two layersof dielectric mirrors and an acoustic-wave-sensing layer between twodielectric mirrors. The ultrasonic-wave-detection laser beam 9700 couldbe in the form of 1-D arrayed laser beams or 2-D arrayed laser beams inother implementations. An optical system that sends out theultrasonic-wave-detection laser beam 9700, detects the reflectedultrasonic-wave-detection laser beam 9700 modulated by photoacousticwaves is skipped from FIG. 9 for simplicity. Spectroscopic photoacousticsignals could be acquired from a one-dimensional or a two-dimensional ora three-dimensional, depth-resolved space in the tissue, and bedigitized and analyzed by the control system 1110 shown in FIG. 1.

FIG. 10 shows another schematic example of a patient interfacecomprising a vacuum structure 10200, a circular arrayed ultrasonictransducer 10400, and an interface medium 10300 in acoustic contact witha tissue 10500. Because a light delivery unit that should be shown inthe patient interface is no different from that of a conventional laserSP system, the light delivery unit is skipped in FIG. 10 for simplicity.Laser beams 10100 (a surgical laser beam, or a temperature-sensing laserbeam, or both) can be selectively delivered to the tissue 10500 surfaceaccording to the requirements of the methods. The circular arrayedtransducer 10400 could be a traditional ultrasonic transducer or onebased on optical detection techniques. The circular arrayed ultrasonictransducer 10400 is in acoustic contact with the wall of the vacuumstructure 10200. The vacuum structure 10200 is designed to suck part ofthe tissue into it in a way similar to a body cupping device. Interfacemedium 10300 such as water could be injected into the bottom of thevacuum structure to immerse the tissue sucked into the vacuum structure.The laser beams 10100 illuminate the tissue inside of the vacuumstructure and excite photoacoustic waves. The circular arrayedultrasonic transducer 10400 could acquire spectroscopic photoacousticsignals from a two-dimensional, depth-resolved space in the tissue. Thecircular arrayed ultrasonic transducer 10400 could be adjusted inelevational direction for acquiring spectroscopic photoacoustic signalsfrom a three-dimensional, depth-resolved space in the tissue. Thespectroscopic photoacoustic signals are digitized and analyzed by thecontrol system 1110 shown in FIG. 1.

FIG. 11 shows an example of wavelength tuning operation for optimizingSP laser treatment of unknown pigments. The optimal surgical laserwavelength should maximize the laser energy deposition ratios of unknownpigments to nature chromophores. The following procedure is designed fora laser SP surgery system whose surgical laser pulse width is shortenough to effectively excite photoacoustic signals. However, if thesurgical laser pulse is too long to effectively excite photoacousticsignals, a short temperature-sensing laser pulse generated by a moreadvanced dual-pulse (a surgical laser pulse followed by a delayedtemperature-sensing laser pulse) laser system should be used to excitephotoacoustic signals in the following procedure. First, a series ofwavelength points that comprises characteristic peaks and valleys ofoxygenated hemoglobin and deoxygenated hemoglobin is determined; Second,a tissue area is selected and the patient interface is operated to be inacoustic contact with the selected tissue area; Third, the acousticdetector is preferably configured in the mode of acquiring a 2-D,depth-resolved photoacoustic tissue information with a single surgicallaser pulse. It is noted that the acoustic detector could be configuredto acquire 1-D, depth-resolved tissue information in a simplifiedimplementation and the following steps might need slight modifications;Fourth, the control system sends out multiple subtherapeutic surgicallaser pulses for each wavelength point, and acquires photoacousticsignals detected by the acoustic detector; Fifth, an averaged 2-D,depth-resolved tissue information is acquired after tomographyreconstruction for each wavelength point; Sixth, unknown pigments areidentified along with nature chromophores after their relativeextinction coefficients are calculated and their relative extinctioncoefficient curves are fitted. If no nature chromophores are presentedin the 2-D, depth-resolved tissue space, known extinction coefficientcurves of nature chromophores from literature could be used; Seventh,relative energy deposition ratio curves of unknown pigments to naturechromophores are calculated; Finally, the optimal surgical laserwavelengths are determined for different types of unknown pigments withan algorithm that puts different priority weights on different naturechromophores. Multiple laser treatments with optimized lasingwavelengths for different types of unknown pigments might be performedin series for the optimal laser treatment outcome. The same technique inFIG. 11 applies to pulsed laser (coherent light source) SP surgicalsystems, other non-coherent pulsed light-source SP surgical systemswhere the central wavelength of the non-coherent pulsed light source istuned, and other general radiation SP systems using awavelength-tunable, pulsed or modulated radiation beam to effectivelyexcite photoacoustic waves from lesions in tissue or extraneous contrastagents attached to lesions in tissue.

For the more advanced dual-pulse (a surgical laser pulse followed by adelayed temperature-sensing laser pulse) laser SP surgical system, thisinvention provides a method for photoacoustic temperature sensing inlive tissue including a non-invasive Grüneisen parameter calibrationprocedure. This method overcome limitations of methods in prior art.This method detailed in FIGS. 12 and 13 can non-invasively measuredynamic temperature of a surgical target in a tissue heated by a shortsurgical laser pulse after calibration. The calibration procedure isbased on a hypothesis that the heating of a surgical target by laserpulses is a linear process and the maximum temperature rise of thesurgical target is proportional to the laser energy deposited into thesurgical target when the temperature is measured immediately after thesurgical laser pulse.

FIG. 12 shows an example of calibrating a temperature-dependent relativelogarithm function of Grüneisen parameter of tissue. First, we startcalibration process by measuring the equilibrium temperature T0 of thetissue; Second, we measure the photoacoustic signal of a surgical targetexcited by a temperature-sensing laser pulse with a constant laser pulseenergy, perform a logarithm operation on the photoacoustic signalamplitude, and get a baseline signal; Third, we send a surgical laserpulse for heating the surgical target and measure the photoacousticsignal excited by the surgical laser pulse; Fourth, we send both thesurgical laser pulse and the temperature-sensing laser pulse, measurethe excited photoacoustic signal by dual pulses, subtract thephotoacoustic signal excited by the surgical laser pulse from that ofthe dual pulses, calculate the amplitude of the photoacoustic signalexcited by the temperature-sensing laser pulse, separatetemperature-dependent part from other temperature-independent parts witha logarithm operation, subtract the baseline signal, and calculate arelative logarithm function value, logΓ(T0+δT)−logΓ(T0) where ┌ denotesthe Grüneisen parameter of the tissue and δT denotes the temperaturerise caused by the heating laser pulse, for the temperature point ofT0+δT; Fifth, if the recorded photoacoustic signal amplitude does notshow an abrupt increase due to the laser-induced cavitation at 100° C.,we wait until the tissue temperature returns to its original equilibriumtemperature. Then we adjust the heating laser pulse energy to its kitimes and return to the third step for acquiring another relativelogarithm function value of logΓ(T0 +kiδT)−logΓ(T0) for the temperaturepoint of T0+kiδT. We should keep the increase of the surgical laserenergy small in order to have a more accurate measurement of 100° C. Ifa laser-induced cavitation is observed, we continue to the final step.In the final step, we have

T0+k0δT<T0+k1δT<T0+k2δT< . . . <T0+kmδT=100° C.

Thus, we can calculate the absolute temperature rises (k0δT, k1δT, kmδT)by each surgical laser pulse and fit the function of logΓ(T)−logΓ(T0)between T0 and 100° C. where T denotes temperature. The equilibriumtemperature could be the body temperature of a patient. It could also bean equilibrium temperature of an ex vivo tissue in an environment ofknown temperature. In practice, laser pulse energy fluctuates from pulseto pulse. Compensation with simultaneous laser pulse energy monitoringis necessary for the procedures above. As long as both the startingtemperature and the temperature to be measured are between T0 and 100°C., the calibrated relative logarithm function Grüneisen parameter oftissue is valid for a temperature sensing operation as detailed below.

FIG. 13 shows an example of dynamic temperature sensing operation ofsurgical targets in a tissue after heating by a short surgical laserpulse. However, if the delay time between the surgical laser pulse andthe temperature-sensing laser pulse is adjusted, the dynamic temperaturevariation profile of a surgical target along time can be accuratelymeasured by repeating the following dynamic temperature sensingprocedure. It is important that we start from a known body temperatureand we know the starting point in the relative logarithm function ofGrüneisen parameter. First, we measure body temperature before lasersurgical intervention; Second, we send a temperature-sensing laserpulse, measure the amplitude of the excited photoacoustic signal at bodytemperature and calculate its logarithm as a baseline signal; Third, wesend only a surgical laser pulse and measure the photoacoustic signalexcited by the surgical laser pulse; Fourth, we send both the surgicallaser pulse and the temperature-sensing laser pulse and measure theexcited photoacoustic signal; Fifth, we calculate the amplitude of thephotoacoustic signal excited by the temperature-sensing laser pulse andseparate temperature-dependent part from other temperature-independentparts with a logarithm operation; Sixth, we calculate the relativelogarithm function value by subtracting the baseline signal; Finally, wedetermine the dynamic temperature at the end of the surgical laser pulsefrom the calibrated relative logarithm function of Grüneisen parameterof tissue. For temperature sensing of a surgical target heated by acontinuous-wave laser, it requires only two measurements of thephotoacoustic signals excited by the temperature-sensing laser pulse atthe body temperature and at a time point during CW laser surgery. Moreaccurate measurement result is expected due to the more accurate,non-invasive calibration method in FIG. 12. The same technique in FIGS.12-13 applies to pulsed laser (coherent light source) surgical systems,other non-coherent pulsed light-source surgical systems,high-intensity-focused-ultrasound therapy systems, and other generalradiation SP systems using a surgical pulsed radiation beam to heat uplesions in tissue or extraneous contrast agents attached to lesions intissue, and a pulsed or modulated temperature-sensing radiation beam toeffectively excite photoacoustic waves from lesions in tissue orextraneous contrast agents attached to lesions in tissue.

In applications such as laser treatment of vascular malformations, it isdesirable to effectively heat a surgical target with laser pulses whoselaser pulse width matches to thermal relaxation time of the surgicaltarget. Most energy of laser pulse will be confined to the surgicaltarget instead of being spread to surrounding healthy tissues. Computersimulation with tissue models and a surgical target's dimensioninformation is the only available method to estimate thermal relaxationtime of a surgical target in tissue in the research field of lasertreatment of vascular malformation. However, FIG. 14 shows an example ofoptimizing surgical laser pulse width by in vivo measurement of thermalrelaxation time of a surgical target in tissue. In addition to thesurgical laser pulse, a temperature-sensing laser pulse is required toperform the task of measuring thermal relaxation time of a surgicaltarget. First, we measure body temperature and the photoacoustic signalof a surgical target at body temperature with a temperature-sensinglaser pulse, and calculate the logarithm of the photoacoustic signal asa baseline signal; Second, we send a subtherapeutic surgical laser pulseand measure excited photoacoustic signal; Third, we send both thesubtherapeutic surgical laser pulse and the temperature-sensing laserpulse with a precise delay time, measure excited photoacoustic signal ofdual pulses, and calculate the amplitude of the photoacoustic signalexcited by the temperature-sensing laser pulse; Fourth, we separatetemperature-dependent part from other temperature-independent parts witha logarithm operation and calculate the relative logarithm functionvalue by subtracting the baseline signal; Fifth, we determine thetemperature of the surgical target at the precise delay time; Sixth, wewait until surgical target temperature returns to body temperature, anddetermine whether there are enough delay time points to fit the curve ofthe surgical target's temperature versus delay time. If there are noenough delay time points, we change the value of the delay time andrepeat the procedures between the third step and the sixth step beforewe can fit the curve of temperature versus delay time and derive thethermal relaxation time of the surgical target. The optimal surgicallaser pulse width is determined to be equal to the measured thermalrelaxation time of the surgical target. The same technique in FIG. 14applies to pulsed laser (coherent light source) SP surgical systems,other non-coherent pulsed light-source SP surgical systems, and othergeneral radiation SP systems using a surgical pulsed radiation beam toheat up lesions in tissue or extraneous contrast agents attached tolesions in tissue, and a pulsed or modulated temperature-sensingradiation beam to effectively excite photoacoustic waves from lesions intissue or extraneous contrast agents attached to lesions in tissue.

In a conventional laser SP surgery, surgical laser pulse energy isselected according to a clinician's past experiences. However, theinclusion of an acoustic detector makes it possible to optimize surgicallaser pulse energy objectively for the first time. For the lasertreatment vascular malformations, the optimal laser pulse energy wouldheat the selected surgical target to a predetermined temperature forphotocoagulation. For applications based on laser photodisruption suchas laser tattoo removal, the optimal surgical laser pulse energy wouldheat a selected surgical target to 100° C. and cause laser-inducedcavitation.

FIG. 15 shows an example of surgical laser pulse energy optimization ina tunable laser during a laser photocoagulation SP surgery. We assumethe laser wavelength is already optimized before laser poweroptimization. First, we select a surgical target with a 2-D, depthresolved tissue information excited by a temperature-sensing laser pulseand acquired by an acoustic detector; Second, we optimize laser pulsewidth after measuring the surgical target's thermal relaxation time;Third, we send a surgical laser pulse and measure excited photoacousticsignal; Fourth, we send both the surgical laser pulse and thetemperature-sensing laser pulse, measure the photoacoustic signalexcited by dual pulses, and calculate the amplitude of the photoacousticsignal excited by the temperature-sensing laser pulse; Fifth, weseparate the temperature-dependent part with a logarithm operation,calculate a relative logarithm function value by subtracting thebaseline signal acquired in previous steps, and determine thetemperature of the surgical target; Sixth, we determine whether thesurgical target reaches a predetermined temperature forphotocoagulation. If not, we wait for the temperature to recover itsoriginal body temperature, increase the laser pulse energy and return tothe third step. If the temperature reaches to a predeterminedtemperature for photocoagulation, we end the operation with theoptimized laser pulse energy for photocoagulation of the surgicaltarget. The same technique in FIG. 15 applies to pulsed laser (coherentlight source) SP surgical systems, other non-coherent pulsedlight-source SP surgical systems, high-intensity-focused-ultrasoundtherapy systems for optimizing ultrasound beam energy, and other generalradiation SP systems using a surgical pulsed radiation beam to heat uplesions in tissue or extraneous contrast agents attached to lesions intissue, and a pulsed or modulated temperature-sensing radiation beam toeffectively excite photoacoustic waves from lesions in tissue orextraneous contrast agents attached to lesions in tissue.

A distinct feature of laser photodisruption is the generation ofacoustic shock-waves due to a laser-induced cavitation. We assume thereis no need to further increase laser pulse energy once the acousticshock-wave due to laser-induced cavitation is observed. For laserphotodisruption in laser tattoo removal application, it is desirable touse a tunable surgical laser instead of a more advanced tunabledual-pulse (a surgical laser pulse followed by a delayedtemperature-sensing laser pulse) surgical laser. FIG. 16 shows anexample of in vivo surgical laser pulse energy optimization during alaser photodisruption SP surgery. The following procedure is designedfor a laser SP surgery system whose surgical laser pulse width is shortenough to effectively excite photoacoustic signals. We assume the laserwavelength is already optimized before laser pulse energy optimization.First, we select a surgical target with a 2-D, depth resolved tissueinformation excited by the surgical laser pulse and acquired by anacoustic detector; Second, we measure the surgical target's thermalrelaxation time and optimize surgical laser pulse width according to thesurgical target's thermal relaxation time; Third, we send a surgicallaser pulse and measure excited photoacoustic signal; Fourth, we drawone point for the curve of photoacoustic signal versus laser pulseenergy and determine whether there is an abrupt photoacoustic signalincrease due to a laser-induced cavitation. If there is no abruptphotoacoustic signal increase, we can wait for the surgical target torecover its original body temperature, increase surgical laser pulseenergy, and return to the third step. If an abrupt photoacoustic signalincrease due to laser-induced cavitation is observed, the optimal laserpulse energy is achieved. The same technique in FIG. 16 applies topulsed laser (coherent light source) SP surgical systems, othernon-coherent pulsed light-source SP surgical systems, and other generalradiation SP systems using a surgical pulsed radiation beam to heat uplesions in tissue or extraneous contrast agents attached to lesions intissue, and excite photoacoustic waves from lesions in tissue orextraneous contrast agents attached to lesions in tissue.

The methods in FIGS. 15 and 16 provide real time control of surgicallaser pulse energy during laser SP surgeries. However, it is possible toaccurately determine the required surgical laser pulse energy for asurgical target to reach a predetermined temperature without actuallyperforming laser surgery. FIG. 17 shows an example of determiningoptimal surgical laser pulse energy to achieve a predeterminedtemperature without performing laser surgery. We assume the laserwavelength is already optimized. First, we select a surgical target witha 2-D, depth resolved tissue information excited by thetemperature-sensing laser pulse and acquired by an acoustic detector;Second, we optimize laser pulse width after measuring the surgicaltarget's thermal relaxation time; Third, we send a subtherapeuticsurgical laser pulse and detect its photoacoustic signal; Fourth, wesend both a subtherapeutic surgical laser pulse and atemperature-sensing laser pulse, which is immediately after the end ofthe surgical laser pulse; Fifth, we measure photoacoustic signal excitedby both the surgical laser pulse and the temperature-sensing laserpulse, and calculate the amplitude of the photoacoustic signal excitedby the temperature-sensing laser pulse; Sixth, we separatetemperature-dependent part with a logarithm operation, calculate arelative logarithm function value by subtracting the baseline signalacquired in previous steps; Finally, we calculate the temperature risedue to the subtherapeutic surgical laser pulse and determine therequired surgical laser pulse energy for heating the target to apredetermined temperature. The same technique in FIG. 17 applies topulsed laser (coherent light source) SP surgical systems, othernon-coherent pulsed light-source SP surgical systems,high-intensity-focused-ultrasound therapy systems, and other generalradiation SP systems using a surgical pulsed radiation beam to heat uplesions in tissue or extraneous contrast agents attached to lesions intissue, and a pulsed or modulated temperature-sensing radiation beam toeffectively excite photoacoustic waves from lesions in tissue orextraneous contrast agents attached to lesions in tissue.

One potential usage of the acoustic detector is to provide in vivotemperature calibration for skin cooling devices that provideprotections for skin epidermis layer in a laser SP surgery. Skin coolingis widely used in laser treatment of vascular malformation. Skin coolingcan effectively prevent laser-induced cavitation in epidermis duringlaser tattoo removal as well. FIG. 18 shows an example of operations foran optimized laser SP surgery with skin cooling. First, we tune thesurgical laser wavelength to maximize SP surgical effects; Second, weoptimize the surgical laser pulse width according to the measuredthermal relaxation time of the surgical target; Third, we optimizesurgical laser pulse energy according to the expected surgical effects(photocoagulation or photodisruption); Fourth, we measure bodytemperature, send a temperature-sensing laser pulse, measure theamplitude of the excited photoacoustic signal of an epidermis target,and calculate its logarithm value as a baseline signal; Fifth, we adjustskin cooling parameter, apply skin cooling, and send a delayedtemperature-sensing laser pulse; Sixth, we measure the amplitude of thephotoacoustic signal excited by the temperature-sensing laser pulse,calculate the relative logarithm function value by taking logarithm andsubtracting the baseline signal; Seventh, we determine the temperatureof the epidermis target and whether the epidermis target is cooled to apredetermined temperature. If not, we wait for temperature recovery andreturn to the fifth step. If yes, we perform optimized SP surgery. Thesame technique in FIG. 18 applies to pulsed laser (coherent lightsource) SP surgical systems, other non-coherent pulsed light-source SPsurgical systems, and other general radiation SP systems using asurgical pulsed radiation beam to heat up lesions in tissue orextraneous contrast agents attached to lesions in tissue, and a pulsedor modulated temperature-sensing radiation beam to effectively excitephotoacoustic waves from lesions in tissue or extraneous contrast agentsattached to lesions in tissue.

Techniques, apparatus and methods for optimizing selectivephotothermolysis laser surgery are disclosed. However, variations andenhancements of the described implementations, and other implementationscan be made based on what is described.

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What is claimed is:
 1. A photoacoustic temperature measurement methodcomprising: calibrating a relative logarithm function of Grüneisenparameter of a media surrounding said target; determining an ambienttemperature of said target; exciting a photoacoustic wave from saidtarget with a laser pulse of constant pulse energy under said ambienttemperature, measuring an amplitude of said photoacoustic wave with anacoustic detector, and calculating a logarithm value of said amplitudeas a baseline signal; applying a temperature changing mechanism andmeasuring a corrective photoacoustic response if necessary; applyingsaid temperature changing mechanism immediately followed by said laserpulse at a desirable delay time, exciting a photoacoustic wave from saidtarget, measuring an amplitude of photoacoustic wave, subtracting saidcorrective photoacoustic response if necessary, calculating a logarithmvalue, and getting a relative logarithm value; determining thetemperature of said target at the desired delay time after applicationof said temperature changing mechanism based on said ambienttemperature, said relative logarithm value and said relative logarithmfunction of Grüneisen parameter of said media.
 2. A method of claim 1,wherein temperature changing mechanism comprises laser heating,electrical magnetic wave heating, acoustic wave heating, cryogen spraycooling and any other forms of temperature changing mechanisms.
 3. Amethod for calibrating a relative logarithm function of Grüneisenparameter of a media surrounding a target comprising: heating saidtarget to a series of temperature points by sending a series of shortheating laser pulses with increasing laser pulse energies until the lastlaser pulse induces photodisruption in tissue and said target reaches100° C.; determining said series of temperature points based on excitedphotoacoustic waves and the linear relationship between temperaturerises and excited photoacoustic waves; calibrating photoacousticresponses of said target by sending temperature sensing laser pulseswith constant pulse energy immediately after said temperature points arereached and correcting photoacoustic responses induced by short heatinglaser pulses alone; determining said relative logarithm function ofGrüneisen parameter of said media surrounding said target.